I'll be flabberghasted it this even runs...

.github/snippets/settings.local.php

@@ -0,0 +1,35 @@
+<?php
+
+/**
+ * @file
+ * Settings file to connect to a local mysql.
+ * Copied into position on GitHub CI runs.
+ */
+
+$databases['default']['default']['database'] = "db";
+$databases['default']['default']['username'] = "user";
+$databases['default']['default']['password'] = "";
+$databases['default']['default']['host'] = "localhost";
+$databases['default']['default']['port'] = "30123";
+$databases['default']['default']['driver'] = "mysql";
+
+
+// This will prevent Drupal from setting read-only permissions on sites/default.
+$settings['skip_permissions_hardening'] = TRUE;
+
+// This will ensure the site can only be accessed through the intended host
+// names. Additional host patterns can be added for custom configurations.
+$settings['trusted_host_patterns'] = ['.*'];
+
+// Don't use Symfony's APCLoader. ddev includes APCu; Composer's APCu loader has
+// better performance.
+$settings['class_loader_auto_detect'] = FALSE;
+
+// Set $settings['config_sync_directory'] if not set in settings.php.
+if (empty($settings['config_sync_directory'])) {
+  $settings['config_sync_directory'] = 'sites/default/files/sync';
+}
+
+// Enable verbose logging for errors.
+// https://www.drupal.org/forum/support/post-installation/2018-07-18/enable-drupal-8-backend-errorlogdebugging-mode
+$config['system.logging']['error_level'] = 'verbose';

.github/workflows/behaviour.yml

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+name: Behaviour Tests
+on: [push]
+
+env:
+  PLATFORMSH_CLI_TOKEN: ${{ secrets.PLATFORMSH_CLI_TOKEN }}
+
+jobs:
+  tests:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v3
+
+      - name: Setup PHP, with composer and extensions
+        uses: shivammathur/setup-php@v2
+        with:
+          php-version: '8.2'
+          extensions: gdate, dom, filter, gd, hash, json, pcre, PDO, session, SimpleXML, SPL, tokenizer, xml
+
+      - name: Composer Install
+        run: |
+          composer --no-interaction --no-progress --optimize-autoloader install
+
+      # Install Psh CLI.
+      - name: Install Psh CLI
+        run: curl -sS https://platform.sh/cli/installer | php
+
+      # If you need to connect to database.
+      - name: Load certificate
+        run: ~/.platformsh/bin/platform ssh-cert:load -y -vvv
+
+      - name: Add Psh to trusted keys
+        run: |
+          ssh-keyscan ssh.uk-1.platform.sh >> ~/.ssh/known_hosts
+          ssh-keyscan git.uk-1.platform.sh >> ~/.ssh/known_hosts
+
+      # Non-database Psh commands.
+      - name: Spin up environment
+        run: ~/.platformsh/bin/platform environment:activate -p XXX -e ${GITHUB_REF#refs/heads/} --yes
+
+      - name: connect to psh PR db
+        run: |
+          nohup platform tunnel:single --project=nlw7xhb3fyt7y --environment=${GITHUB_REF#refs/heads/} --port=30123 --relationship=database --yes & > phpd.log 2>&1 &
+
+      - name: Drupal config to access db
+        run: |
+          cp ./.github/snippets/settings.local.php ./web/sites/default/settings.local.php
+
+      # Finally, run the tests.
+      - name: Run Behat tests
+        run: |
+          ./vendor/bin/behat
+
+      - name: Tear it all down
+        run: |
+          platform tunnel:close   --project=nlw7xhb3fyt7y --environment=${GITHUB_REF#refs/heads/} --yes